Pathways for water oxidation catalyzed by the ((bpy) sub 2 Ru(OH sub 2 )) sub 2 O sup 4+ ion

Journal Article · Wed Mar 18 04:00:00 EST 1992 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00032a017· OSTI ID:6967741

Hurst, J K; Zhou, Jinzhong; Lei, Yabin ^[1]

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1. Oregon Inst. of Science and Technology, Beaverton (United States)

Resonance Raman (RR) spectra of the ({mu}-oxo)bis(cis-aquabis(2,2{prime}-bipyridine)ruthenium(III)) ion and its congeners in thermodynamically accessible III-IV, IV-V, and V-V higher oxidation states have been obtained in aqueous solutions under a wide range of medium conditions. The RR spectra were dominated by single bands at 370-403 cm{sup {minus}1}, assignable to the Ru-O-Ru symmetric stretching mode ({nu}{sub s}) on the basis of their {sup 18}O-isotope induced shifts. From the magnitudes of the shifts, the Ru-O-Ru angles were calculated to be 155-180{degree} for the various oxidation states. A band appearing at 812 cm{sup {minus}1} in the V-V ion which shifted to {approximately} 780 cm{sup {minus}1} in ({sup 18}O)H{sub 2}O was assigned to a Ru{double bond}O stretching mode of a terminal oxo ligand. Below pH 0.3 the bridging {mu}-oxo atom became protonated; for the other ions, hydrogen bonding to the bridge was indicated by D{sub 2}O-induced solvent shifts in {nu}{sub s}(Ru-O-Ru). An {sup 18}O-isotope labeling study of the water oxidation reaction established the existence of a pathway in which one atom of O{sub 2} was obtained from an aqua ligand. These results combined with published rate data suggest that this pathway involves solvent nucleophilic attack of a terminal oxo atom as the critical oxygen-oxygen bond forming step, with the bridging oxygen atom serving the essential role of activating and/or orienting the reactant H{sub 2}O through formation of a strong hydrogen bond. A second major pathway, for which both O atoms were derived from solvent, was also identified, but no definitive evidence was obtained for a pathway for which both O atoms originated in coordinated H{sub 2}O.

• DOE Contract Number: FG06-87ER13664
• OSTI ID: 6967741
• Journal Information: Inorganic Chemistry; (United States), Journal Name: Inorganic Chemistry; (United States) Vol. 31:6; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
080102* -- Hydrogen-- Production-- Thermochemical Processes
AQUEOUS SOLUTIONS
CATALYTIC EFFECTS
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMATOGRAPHY
COMPLEXES
DISPERSIONS
ELEMENTS
EVEN-EVEN NUCLEI
GAS CHROMATOGRAPHY
HYDROGEN COMPOUNDS
IONS
ISOTOPE RATIO
ISOTOPES
KINETICS
LIGANDS
LIGHT NUCLEI
MASS SPECTROSCOPY
MIXTURES
NONMETALS
NUCLEI
OXIDATION
OXYGEN
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PH VALUE
RAMAN SPECTRA
REACTION KINETICS
REDOX REACTIONS
RUTHENIUM COMPLEXES
SEPARATION PROCESSES
SOLUTIONS
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
VALENCE
WATER